Sample injection arrangement for an analytical instrument

ABSTRACT

A sample injector arrangement for an analytical instrument includes a septum body which is shielded from the environment of a sample injection chamber by a shielding means positioned between the septum and the chamber and having a channel extending therethrough along its length between the septum at one end and a gas flow path at an opposite end. The channel is adapted for receiving a sample injection probe and provides a means of minimizing the surface area of the septum which is exposed to the sample chamber. An injector arrangement adapted for further reducing ghost peaks includes a plurality of channel members adapted for extending the diffusion path between dead volume and the injector and the septum.

1U nite States Patent Downs et al,

1451 Alan, 1,, 1977 [54] SAMPLE INJECTION ARRANGEMENT F0 AN ANALYTICAL INSTRUMENT [72] Inventors: Horace Dean Downs, North Haven; John E. Purcell, Old Greenwich, both of Conn.

The Perkin-Elmer Corporation, Norwalk, Conn.

[22] Filed: May 29,1969

[2|] Appl.No.: 829,004

[73] Assignee:

[52] US. Cl. ..73/422 GC [51] llnt. Cl ..G01n 11/22, GOln 3l/08 [58] Fleldol'Senrch ..73/42l,23,23.1,53,6l.l C, 73/422 GC; 23/252, 254

[56] References Cited UNITED STATES PATENTS 3,537,321 11/1970 La Barre ..73/422 GC 2,991,647 7/1961 Harris ...73/422 GC 3,327,520 6/1967 StaPP, Jr ..73/23 1 3,374,660 3/1968 McKinney et al. ...73/422 0c x 3,463,012 8/1969 McKinney et a1. ..73/422 cc FOREIGN PATENTS OR APPLICATIONS 971,678 9/1964 Great Britain ..73/422 GC OTHER PUBLICATIONS Journal of Scientific Instruments 1965, Vol. 42, page 47, A Simple Injection Port and Column Holder for Use in Gas Chromatography" by Arnold et al., Q184J7 Primary Examiner-Louis R. Prince Assistant Examiner-Daniel M. Yasich Attorney-Edward R. Hyde, Jr.

[5 7 ABSTRACT A sample injector arrangement for an analytical instrument includes a septum body which is shielded from the environment of a sample injection chamber by a shielding means positioned between the septum and the chamber and having a channel extending therethrough along its length between the septum at one end and a gas flow path at an opposite end. The channel is adapted for receiving a sample injection probe and provides a means of minimizing the surface area of the septum which is exposed to the sample chamber. An injector arrangement adapted for further reducing ghost peaks includes a plurality of channel members adapted for extending the diffusion path between dead volume and the injector and the septum.

1 Claims, 7 Drawing Figures SAMPLE INJECTION ARRANGEMENT FOR AN ANALYTICAL INSTRUMENT This invention relates to analytical instruments. The invention relates more particularly to improved means for introducing a sample under analysis to an analytical instrument.

In a copending U.S. Pat. application, Ser. No. 693,926, filed on Dec. 27, 1967, and now U.S. Pat. No. 3,581,573, and which is assigned to the assignee of this invention, the problem of septum bleed in an analytical instrument is discussed. Briefly, a septum, which is a body formed of a probe-penetrable, self-sealing material is employed as a wall member of a gas flow path in an analytical instrument such as a gas chromatograph. The septum provides for the introduction into the gas flow path of a sample under analysis through the use of a hypodermic syringe. Although the septum is formed of a relatively inert material such as silicone rubber, nonetheless the septum exhibits a tendency to exhaust volatile components which are constituents of the septum material, or which are sample components which have been adsorbed by the septum during previous use. These components create "ghost peaks" which will interfere with the analysis in a sensitive instrument during temperature programming of the instrument.

An arrangement for reducing septum bleed is disclosed in the referred-to copending application wherein a body, formed of a relatively inert material and which is penetrable by a sample probe, is positioned for shielding the injector chamber from the septum material. In one arrangement a disc is provided as a shielding body. An alternative embodiment employs a strip of shielding material which is adapted to be advanced along the surface of the septum body subsequent to each sample injection. While these shielding arrangements are advantageous for eliminating ghosts, it has been found desirable to replace the shielding disc after each sample injection. In addition, the use of an advancing arrangement for disposing a shielding body adjacent the septum results in a relatively complex injector cap. Thus, while the shielding arrangements are operationally advantageous, they are inconvenient for the instrument operator.

It is an object of this invention to provide an improved arrangement for shielding a septum body from an injector chamber in an analytical instrument.

Another object of this invention is to provide an improved septum shielding arrangement which can be utilized for repeated sample injection while eliminating the need for replacement of, or, advancement of the shielding body.

The existence of dead volumes in an injector apparatus can result in the retention of sample components of previous analyses and contributes to the creation of undesirable ghost pealrs.

A further object of this invention is to provide an improved injector arrangement adapted for establishing a relatively elongated diffusion path between a septum body and a dead volume of the sample injector.

In accordance with a feature of the present invention, a septum body in an analytical instrument is shielded from the sample injection chamber environment by a shielding means positioned between the septum and chamber and having a channel extending therethrough along its length between the septum at one end and a gas flow path of the instrument at an opposite end. The channel is adapted for receiving a sample injection probe and provides relatively minimal communication between the septum and chamber. The shielding means is further adapted to provide a gastight seal between members of the sample injector.

In accordance with another feature of the invention, the diffusion path of the channel is substantially eliminated by a valving means adapted for interrupting gas flow passage through the channel.

. A sample injector arrangement having a dead volume and constructed in accordance with features of this invention comprises an injector assembly having a plurality of elongated members arranged for defining an elongated upstream carrier fluid flow path between the dead volume and the location of sample introduction. In a particular arrangement the dead volume is positioned adjacent to but isolated from the septum, and the members comprise concentric-ally positioned tubular bodies arranged for causing the carrier fluid to flow over a path extending in a direction geometrically away from the septum to a location at which the carrier fluid flow path then extends geometrically toward the septum. With this arrangement, an efficient sweeping of the injector by the carrier fluid is accomplished while a diffusion path between the dead volume located upstream from the septum and the septum itself is substantially increased.

These and other objects and features of the invention will become apparent with reference to the following specifications and the drawings, wherein:

FIG. I is a block diagram of a chromatographic analytical instrument incorporating features of the present invention;

FIG. 2 is a sectional view of the injector of FIG. I illustrating an embodiment of the present invention;

FIG. 3 is a sectional view of the injector cap and septum shielding means of FIG. 2 constructed in accordance with an alternative embodiment of the present invention;

FIG. 4 is a sectional view of the injector cap and septum shielding means of FIG. 2 constructed in accordance with another alternative embodiment of the present invention;

FIG. 5 is a sectional view of the injector cap and septum shielding means of FIG. 2 constructed in accordance with a further alternative embodiment of the present invention;

FIG. 6 is a view of the injector cap and septum shielding I means of FIG. 2 constructed in accordance with still another embodiment of the present invention; and,

FIG. 7 is a sectional view taken along line 77 of FIG. 6.

Referring now to FIG. 1, an analytical instrument is shown to comprise a gas chromatograph having a separating column 10, an injector block 12 for introduction to the instrument of a liquid or gaseous sample material by a syringe 14 at an injector station 16, a source of carrier gas 18 for conveying the sample from the injector block to the separating column 110, and a detector 20 and a recorder 22 for respectively detecting and providing a recorded indication of the separated components of the sample which elute successively in time from the column 10.

The injector block 12, which is shown in greater detail in FIG. 2, includes an elongated tubular injector body 24 mounted within a heater block 26. Electrical heater coils, not shown, are mounted in the block 26 for heating the injector body 24 andcausing vaporization of liquid samples. Elongated coaxially positioned tubular flow channel members 28 and 30 are located within the injector body 24. Channel member 28 is formed of stainless steel and includes a flanged end 32 extend ing outwardly from the axis of this member for centering this end of the member within the bore of the member 24. Dimples 33 are formed in the channel member 23 and extend inwardly near each end thereof for centering the tubular glass member 30 within its bore. The dimples are spaced at approximate intervals around the inner surface of the member 2%. The glass member 30 which is positioned within the member 28 for the greater part of its length includes an external segment 34 of enlarged diameter having a tapered end surface 36 for aligning the bore of member 30 with an outlet aperture 38 of the injector body 24. A helical spring 39 is positioned about the member 30 and forces the segment 34 into engagement with that surface of the injector body 24 defining the aperture 3b and forces the flanged end 32 of member 28 against a septumsealing body located at an aperture 40 of the injector body 24. This septum-sealing body is discussed in more detail hereinafter. The injector body 24 further includes a tubular carrier gas inlet 41 for conducting carrier gas from the source 18 (FIG. 1) to the interior volume of the injector body.

The carrier gas flow path in this injector assembly is traceable through the tubulation 41 toward the: left as viewed in FIG. 2 between an inner surface of the injector body 24 and an outer surface of the tubular member 28, and then to the right between the inner surface of member 28 and the outer surface of member 30 toward a septum shielding means. A syringe probe 14 (FIG. 1) is introduced through a septum S and disposes a sample within the bore of the member 30 downstream of a conically shaped aperture 42 of this member. The carrier gas then sweeps this sample to the left as viewed in FIG. 2 through the bore of member 30 to the aperture 38 and to the separating column of the instrument. In this arrangement then, a dead volume which disadvantageously can trap contaminants and sample components exists in that space to the right of the inlet tube 41 as defined by the flange 32, the inner surface of injector body 24 and the outer surface of the tube 28. An elongated upstream flow path is thereby provided between the dead volume and the sample entry station. This elongated upstream flow path represents an extended diffusion path for sample components between this dead volume and sample entry station, and it thereby advantageously results in a substantial reduction of ghost peaks.

A demountable annular cap 44 having integral cooling fins extending therefrom is screwed to an outer surface of the injector body 24 at the aperture 40. A channel 46 terminating in a tapered entrance aperture 48 is formed in the cap 44. The channel 46 is sealed from the gas flow path of the chamber environment by a cylindrically shaped, probe-penetrable, selfsealing septum body 50 which is positioned within the cap adjacent this channel. The septum body 50 is typically formed of a silicone rubber. As indicated hereinbefore, the septum body 50 undesirably exhausts volatile components into the carrier gas stream during temperature programming and at times releases materials into the stream which had been adsorbed during a prior analysis, thereby resulting in ghost peaks which interfere with the present analysis.

In accordance with a feature of this invention, an improved septum shielding means is provided for shielding the septum body 50 from the gas flow stream and the environment of the injector. The septum shielding means comprises an elongated body 52 which is formed of a substantially inert material and which is positioned against an inner surface of the septum body 50. The shield 52 includes a channel 54 for receiving the sample probe. This channel is relatively small in bore, and this small bore provides a relatively minimal diffusion path for molecular gas flow between the septum body 50 and the interior of the injector contained within the member 28. During sample injection, the channel 54 is substantially occupied by the syringe needle thus further reducing flashing sample from contacting the septum. In a particular shield arrangement, the shield body 52 is fabricated of a fluorocarbon resin (polytetrafluordethylene) and includes a channel 54 having a bore of 0.033 inches and a length of 0.250 inches. In prior shielding arrangements repeated use of a same shielding disc results in a greatly enlarged shield aperture which provides relatively little isolation between the carrier gas and the septum body 50. The preformed channel 54 of the shield body of the present invention establishes a guide in the body for the syringe needle, thereby rendering variations in its diameter negligible. The accompanying communication greatly reduces communication between the carrier gas and the septum body. The need for replacement of the prior art disc shield devices after each analysis is avoided and the instrument operator is thereby freed from this task.

The septum shield of FIG. 2 further includes a metal insert 56 having a tapered entrance aperture 58 and a channel segment aligned with the channel 54 of the Teflon shield body 52. The probe is thereby guided through the shield channel by a metal surface and the entrance aperture to the shield is maintained at a desired constant value. An integral shoulder 62 is formed in the body 52 and functions to provide a gastight seal between the injector body 24 and the septum body 50.

FIG. 3 illustrates an alternative embodiment of the invention. Elements of the injector arrangement in FIG. 3, FIG. 4, FIG. 5, FIG. 6 and FIG. 7 which perform similar functions as recited with respect to the injector of FIG. 2 bear the same reference numerals. The shield body 64 of FIG. 3 is formed of metal such as stainless steel for example and includes a tapered entrance aperture 65 formed integrally therein and a shoulder 66. A gastight seal is provided with this embodiment by a relatively inert material such as a fluorocarbon resin which is shaped as a washer 68 and positioned about the shield 64. The washer 68 provides a gastight seal between the body 24 and the shield body 64.

FIG. 4 illustrates another embodiment of the invention wherein the shielding means is formed of metal such as stainless steel and a gastight seal between the injector body 24 and the shield 70 is provided by a bonnet-shaped member 72 formed of an inert material such as a fluorocarbon resin. In this arrangement the member 72 also extends axially along the length of the shield and provides a gastight seal between the inner surface of the injector body 24 and the shield member 70.

FIG. 5 illustrates a further embodiment of the invention wherein the shielding means is formed of metal and is brazed to the tubular body 28. A washer 76 of inert material such as Teflon is positioned about this assembly and provides a gastight seal between the injector body 24 and the shield 74.

FIGS. 6 and 7 illustrate an alternative embodiment of the invention which is adapted for interrupting the gas flow passage through the shield body channel and thus substantially reduces to zero the communication between the septum and the carrier gas flow path. The septum shield means includes a first cylindrically shaped member 80 of inert material such as Teflon having a portion of the channel 54 extending through its length, and, a second generally cylindrically shaped member 82 having a portion of the channel 54 extending also through its length. The member 82 includes an integral shoulder segment 84 which forms a gastight seal between the injector body 24 and a sliding valve member 86. Valve member 86 comprises a panel having a width extending over the diameter of the shield bodies 80 and 82 and having a channel 88 extending through its thickness. This channel terminates in a tapered entrance aperture on that portion of the panel adjacent the shield member 80. A slot is formed in the cap 44 for providing movement of the panel 88 in a direction perpendicular to the axis of the cap. This slot, the thickness of the valve 88 and the abutting members of the septum shield provide a frictionally tight valving member which can be moved by the application of force to either of its extremities. An indexing stop pin 90 and an indexing stop pin 92 are provided for limiting the travel of the valve 86 in the cap 44. In the position shown in FIG. 6, the pin 92 abuts the upper cooling fins when the channel 88 is off axis, thereby interrupting a continuous channel between the septum 50 and the chamber. When the valve is in this position, the mean-free path between the septum and the chamber is substantially zero. Movement of the valve 86 in the opposite direction so that the pin 90 abuts the upper portion of the cooling fin will result in alignment of the valve channel 88 with the channel 54 of the members 80 and 82. The injector is then conditioned for receiving the syringe probe. This arrangement is particularly advantageous in that the communication between the septum and the chamber is substantially zero except during those times when the sample is being introduced. Although the members 80 and 82 are shown to have substantially equal thickness, the member 80 can be replaced by a disc formed of inert material while the member 82 is substantially increased in thickness. Alternatively the member 80 is substantially increased in thickness while the member 82 is reduced to a thickness sufficient for providing a gastight seal between the injector body 24 and the valve 86. In a further alternative arrangement, the valve arrangement of FIGS. 6 and 7 comprises a rotary-type valve or other means for interrupting channel An improved arrangement has thus been described for reducing septum bleed into the gas flow stream of an analytical instrument. The described arrangement is particularly advantageous since it can be repeatedly utilized and avoids the necessity for an immediate replacement which is characteristic of prior art devices. The diffusion path in the injector assembly is advantageously extended to thereby reduce communication between dead volumes in the injector apparatus and the septum.

While we have illustrated and described a particular embodiment of our invention, it will be understood that various modifications may be made therein without departing from the spirit of the invention and the scope of the appended claims.

We claim:

1. In an analytical instrument, a sample injection arrangement comprising;

an elongated injector body having a channel extending therethrough and terminating at a sample inlet aperture at a first end thereof and an outlet aperture at a second end thereof;

means including a probe-penetrable, self-sealing wall material for providing access to the interior of said channel for introducing a sample thereto and for providing a gastight closure at said first end;

a carrier gas inlet passage formed in said body along said length near said first end;

a first elongated tubular member positioned within said channel and spaced from an inner :surface of the channel for providing a gas flow passageway therebetween;

a second elongated tubular member positioned within said channel and extending coaxially within said first member for forming a gas flow passage between said first and second members; and

spring biasing means for forcing said first tubular member against a gastight seat at said first end of said elongated body and for forcing said second tubular member against a gastight seat at said second end of said tubular body to thereby provide a gas flow passage between said tubular members. 

1. In an analytical instrument, a sample injection arrangement comprising: an elongated injector body having a channel extending therethrough and terminating at a sample inlet aperture at a first end thereof and an outlet aperture at a second end thereof; means including a probe-penetrable, self-sealing wall material for providing access to the interior of said channel for introducing a sample thereto and for providing a gastight closure at said first end; a carrier gas inlet passage formed in said body along said length near said first end; a first elongated tubular member positioned within said channel and spaced from an inner surface of the channel for providing a gas flow passageway therebetween; a second elongated tubular member positioned within said channel and extending coaxially within said first member for forming a gas flow passage between said first and second members; and spring biasing means for forcing said fiRst tubular member against a gastight seat at said first end of said elongated body and for forcing said second tubular member against a gastight seat at said second end of said tubular body to thereby provide a gas flow passage between said tubular members. 